Fiber optics have provided a substantial increase in the volume of data that networks can carry. Synchronous Optical Network (SONET) is a standard that defines data transmissions over fiber optics. SONET defines a number of different data rates for different levels of service. A typical SONET network can carry from about 52 megabits per second up to about 10 gigabits per second over a single optical fiber. In comparison, a typical analog modem operating at maximum efficiency can achieve a mere 56 Kilobits per second. At the 10 gigabit SONET rate, a single optical fiber can carry enough data to handle well over 100,000 simultaneous voice calls. SONET networks are likely to carry even larger volumes of data in the future.
Data in a SONET network is often processed in electrical form. For instance, a SONET network may be made up of a web of optical fibers interspersed with routers and/or switches. The routers and/or switches determine which path data should take to reach a particular destination. Optical data is usually converted to electrical form before being processed by a router or switch. If a router or switch determines that data is to continue on through the SONET network, the data is converted back to optical form before being passed on to the next router or switch. Data may pass through many routers and/or switches between a source and a destination.
Data is also converted to and/or from optical form at the edges of a SONET network. For example, routers and/or switches may connect one or more electrical networks to one or more SONET networks. Data may start out in electrical form to travel over wires making up an electrical network, get converted by routers and/or switches back and forth between electrical and optical form while traveling among various SONET networks and/or additional electrical networks, and eventually travel in electrical form over wires leading to a destination.
Each time data enters or leaves a SONET network, or gets processed in electrical form within a SONET network, the data is usually converted to/from a particular SONET frame format. The frame format depends on the physical characteristics of the particular SONET medium. Different media can support different sizes of SONET frames, and therefore different volumes of data.
In the past, the electrical hardware used to convert data to and/or from SONET frames has been matched to the corresponding physical SONET medium. That is, if the SONET medium supports 52 megabits per second, a framer is used that converts frames at 52 megabits per second. If the SONET medium supports 10 gigabits per second, a framer is used that converts frames at 10 gigabits per second. If, for any reason, a different data rate is needed or desired, new hardware is required, often requiring considerable additional expense.